1. Field of the Invention
This invention relates to regenerating an exhaust gas treatment device and more particularly relates to regenerating the exhaust gas treatment device with reduced reductant and hydrocarbon slip.
2. Description of the Related Art
Engines that derive energy from combustion such as internal combustion engines produce an exhaust gas. The exhaust gas may include one or more undesirable emissions (hereinafter emissions) such as nitrogen oxide (“NOX”), carbon monoxide, and the like. Internal combustion engines such as diesel engines, gasoline engines, and the like often have exhaust systems with exhaust gas treatment devices such as catalytic converters to remove emissions from exhaust gas.
In one embodiment, a catalytic converter may be a NOX adsorber. The NOX adsorber adsorbes NOX from the exhaust gas onto a site of the NOX adsorber by oxidizing the NOX to create a nitrate. The nitrate remains on the NOX adsorber site, preventing the release of the NOX into the atmosphere.
NOX adsorbers may function more efficiently if regenerated. During regeneration the nitrate is driven from the NOX adsorber site and converted to nitrogen. Injecting a reductant into the exhaust gas typically regenerates NOX absorbers. The reductant creates a reductant to oxygen ratio with an excess of reductant in the exhaust gas. Excess reductant drives the nitrates from the NOX absorber site and converts the nitrates to nitrogen. Reductants typically include aqueous urea, hydrocarbon fuels such as diesel fuel, and the like.
Unfortunately, injecting the reductant into the exhaust gas to regenerate the exhaust gas treatment device consumes reductant, increasing the cost of operating the engine. In addition, some of the reductant used in regeneration is not consumed and passes into the atmosphere as hydrocarbon slip, potentially increasing one type of emission.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method regenerate an exhaust gas treatment device using reductant more efficiently and with reduced hydrocarbon slip. Beneficially, such an apparatus, system, and method would reduce the expense and emissions from operating engines.